Abstract
A near eutectoid (0.72 wt% carbon) steel was subjected to controlled cooling in a dilatometer. Increasing cooling rate led to progressive microstructural evolution: from reconstructive pearlite (with decreasing interlamellar spacing) to displacive martensite (of diminishing grain size but enhanced acicularity). The martensite obtained at the fastest cooling (100 Ks−1) was also subjected to tempering. The corrosion performance of specimens with different microstructures was then evaluated using electrochemical (potentiodynamic polarization and electrochemical impedance spectroscopy) tests. The aqueous corrosion rate varied (i) non-linearly with pearlite spacing but (ii) linearly with features of the martensite microstructure. The non-linear dependence of corrosion on pearlite spacing was attributed to alignment or branching-induced interface crystallography. The corrosion current in martensitic or tempered martensite structures scaled linearly with increased martensite grain or lath size but decreased c/a ratio. A clear correlation between electrochemical responses and local depth of attack was also established.
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